To my surprise Explorer GT40s arent drilled for smog, I would know, but I passed my final emssions test with high flow cats. I didnt have the thermactor system hooked up to the back of the heads because there is no provision for the pipe.
I dont know if you have to have an inspection though, if my state had inspections I would've JB welded the pipe to the heads.
I just drilled holes in the thermactor pipe so I could mount it to the back of the heads. We have visual inspection only and I've already been to the test station and they said it was good to go.